1. Field of the Invention
The present invention relates to a belt for a continuously variable transmission, comprising a plurality of metal elements, each of which has front and rear main surfaces for contact with adjacent ones of metal elements, and which are supported on a metal ring assembly with the rear main surface of the preceding metal element being in contact with the front main surface of the succeeding metal element. The belt is wound around a drive pulley and a driven pulley to transmit a driving force between the pulleys.
2. Description of the Prior Art
As shown in FIG. 13, in a belt-type continuously variable transmission having a metal belt 03 wound around a drive pulley 01 and a driven pulley 02, a stationary pulley half 04 of the drive pulley 01 and a stationary pulley half 05 of the driven pulley 02 are positioned in diagonal positions, and a movable pulley half 06 of the drive pulley 01 and a movable pulley half 07 of the driven pulley 02 are positioned in diagonal positions. Therefore, when the movable pulley halves 06 and 07 of the drive pulley 01 and the driven pulley 02 are moved toward or away from the stationary pulley halves 04 and 05, the center line La of a V-groove in the drive pulley 01 and the center line Lb of a V-groove in the driven pulley 02 are misaligned with each other to produce a small misalignment xcex1 (usually equal to or smaller than 1 mm).
There is a continuously variable transmission known from Japanese Patent Application Laid-open No. 4-362338, in which in order to wind a metal belt 03 around the drive pulley 01 and the driven pulley 02 with such misalignment a absorbed, at least one of front and rear contact surfaces of the metal elements 08 forming the metal belt 03 is formed into an arcuate shape, whereby a relative yawing between the metal elements 08 contacting with each other is made possible.
However, the continuously variable transmission described in Japanese Patent Application Laid-open No., 4-362338 suffers from a problem that when the metal elements 08 are wound around the pulley 01 or 02 as shown in FIG. 14, such metal elements 08 are yawed, because relative yawing between the metal elements 08 is possible. This causes a large load to be produced between the metal element 08 and a V-face of the pulley 01 or 02, resulting in a degraded durability.
There is also a continuously variable transmission known from Japanese Utility Model Publication No. 5-37068, in which each front and rear main surface of a metal element is formed into a corrugated sectional shape, wherein the corrugated main surface of the preceding metal element and the corrugated main surface of the succeeding metal element are fitted with each other. In this continuously variable transmission, the relative yawing between the metal elements is prevented and hence, a large load can be prevented from being produced between the metal elements and the V-face of a pulley, thereby providing an enhanced durability.
However, the continuously variable transmission described in Japanese Utility Model Publication No. 5-37068 suffers from a problem that it is difficult to absorb a misalignment produced between the drive pulley and the driven pulley, because the relative yawing between the metal elements is inhibited, and the relative lateral sliding movement between the metal elements is inhibited.
If the entire main surface of each of the metal elements is formed into a completely flat surface, it is possible to prevent adjacent ones of the metal elements from being yawed relative to each other in a state in which they have been wound around the pulley, thereby providing an enhanced durability, and it is possible to permit the relative lateral sliding movement of the adjacent ones of the metal elements in a chord section between the pulleys, thereby absorbing the misalignment. However, it is difficult to form such a metal element only by a punching process, and it is difficult in respect of the cost to finish the main surface into a flat shape by subjecting the metal element to cutting or machining after the punching.
Accordingly, it is an object of the present invention to ensure that the yawing of the metal elements can be prevented, while enabling the absorption of the misalignment by designing the shape of main surfaces of the metal element.
To achieve the above object, according to the present invention, there is provided a belt for a continuously variable transmission having a drive pulley and a driven pulley, comprising a plurality of metal elements, each of which has front and rear main surfaces capable of being brought into contact with adjacent ones of metal elements, and which are supported on a metal ring assembly with the rear main surface of a preceding metal element being in contact with the front main surface of a succeeding metal element. The belt is wound around the drive pulley and the driven pulley to transmit a driving force between the pulleys. One of the front and rear main surfaces of the metal elements has protrusions projecting forwards or rearwards, formed at predetermined locations at laterally opposite ends in a region near a rocking edge, respectively, and the other of the front and rear main surfaces of the metal elements has flat surface portions with which the protrusions are in contact, the flat surface portions being formed at least at laterally opposite ends in a region near a rocking edge, respectively, so that they are perpendicular to the forward and rearward directions.
With the above arrangement, the rear main surface of the preceding metal element and the front main surface of the succeeding metal element are in contact with each other at the protrusions which project forwards or rearwards on one of the front and rear main surfaces at the predetermined locations, at the laterally opposite ends, in the region near the rocking edge, and at the flat surface portions formed on the other main surface, at least at the laterally opposite ends in the region near the rocking edge. Therefore, the metal elements can be wound around each of the pulleys in a correct attitude without yawing, whereby they can be prevented from being damaged. In addition, the flat surface portions on the other main surface are formed, so that they are perpendicular to the forward and rearward directions and hence, the protrusions of one of the front and rear main surfaces can freely slide laterally with respect to the flat surface portions. Therefore, even if misalignment occurs between the drive pulley and the driven pulley, the metal elements can freely slide laterally and be brought into engagement with the drive pulley or the driven pulley in a correct attitude.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.